Rendering Road Intersections

General talk
1

I have been working on my Master Thesis which is a 3D City Generator taking OSM xml data as input. I am having problems while trying to render road intersections. There are bunch of different conditions for intersections and I wonder if there is an existing library or algorithm for drawing all possible different cases. I try to handle as much as I can but there is always some weird intersections as in the example image below that my code cannot handle :

Btw, my project is open source and you can access by the following link, there exist also several screenshots to show capabilities of my project
https://bitbucket.org/CagkanToptas/polimi-osm-city-engine-unity3d/

2

Good job, your screenshots look awesome! Can you post a link to the same intersection in OSM? Do you currently have any intersection related code or simply draw road textures?

3

Here is the image of place from OSM map : (http://www.openstreetmap.org/#map=18/45.80201/9.08500&layers=Q)

What I did till now is to handle all 2 and 3 highway intersections and some cases of 4 way intersections.

  • 2 highway intersection was not difficult. I applied simple vector geometry and link the two road

  • 3 highway was a bit complicated. There are 2 main case in this situation.
    1. 2 different roads, one of them intersect from a middle node
    2. 3 different roads, all of them intersect either from end/start

  • 4 highway even has more conditions like
    1. 2 different roads, both intersect from a middle node
    2. 3 different roads, one of them intersect from a middle node others from end/start
    3. 4 different roads, all of them intersect either from end/start

The image I posted has 5 intersection which consist of 4 different roads, 1 of them intersect from a middle node and others intersect from the end/start

Because of this, I started to think probably there will be cases in somewhere around world which there is even more than 5 intersection at a time. So my question is actually how Openstreetmap render the highways in their tiles from Xml file ? Is the source code available?

4

Basically, an intersection is just an asphalt area without lane markings. Quick and dirty way to do that is leave your roads as they are, then build a new polygon covering the intersection area, and give it asphalt texture without white lines.

This should work for any number of roads.

OSM uses Mapnik for 2d tile rendering:
http://wiki.openstreetmap.org/wiki/Mapnik
http://github.com/mapnik/mapnik

5

I had exactly the same issue in my project (see topic I created). I developed solution proposed by shrddr, but my implementation had bugs and wasn’t performance optimized. Finally, I made roads to be part of terrain mesh

6

There is also a proposal to map the intersections by hand, instead of computing their shapes at rendering stage: http://wiki.openstreetmap.org/wiki/Proposed_features/Street_area